1. Field of the Invention
This invention relates to electromagnetic switches selectively operable under electromagnetic drive and more particularly to those of the integrated type designed for maximum component density.
2. Description of the Prior Art
Reed switches, which include a pair of contacts sealed in a glass tube or the like, have previously been known as one form of electromagnetic switch selectively operable under electromagnetic drive and are being employed in electronic switching systems of communications networks as contact elements in the speech path. In fact, in such switching systems, the capacity of the switch frame for the speech path which employ reed switches amounts to about two-thirds of all the frames required, and it has been difficult to reduce the fabrication cost of such switching systems as the switches including reed switches consisted of a large number of discrete component parts.
Further, in U.S. Pat. No. 3,150,244, issued Sept. 22, 1964, there is disclosed a multiple element type relay which includes a number of core members fixedly inserted in a metal plate perpendicular to the plane thereof through the medium of glass seals and associated with the respective switch elements of the relay. Provided on the metal plate is a cover which is connected hermetically sealed therewith and to which spring strips are welded on the inside thereof to support respective moveable contacts.
With such a switch structure, however, since the cover, serving as gas-tight sealing means, also serves as a signal line common to the moveable contacts, it is difficult to form a matrix switch including a multitude of relays and moveable contacts thereof arranged in a matrix array in which the moveable contacts are electrically connected in series, for example, by lines of the matrix so that the lines of moveable contacts may be utilized independent of each other.
Again, with the switch structure, in which the base plate is metallic and the cores themselves serve as signal lines, wiring connections of such signal lines and magnetizing coils cannot be made on the base plate and necessitates use of some additional means such as a printed circuit board provided exteriorly of the switch proper. This results in the increase in number of component parts as well as in the cost of fabrication and renders the use of such switch structure unadvisable for the realization of any high density integrated switching device.
Moreover, the switch structure, in which respective core members are inserted in the metallic base plate and fixed in position by a glass seal means, necessitates a complicated fabricating process for glass-sealing the core members, which involves the danger that the core members will be deteriorated in magnetic quality at the elevated temperatures employed.